Implantable Intervertebral Fusion Device

ABSTRACT

The present application relates to an implantable intervertebral fusion device for use when surgical fusion of vertebral bodies is indicated. The implant is comprised of bone conforming in size and shape with the end plates of the adjacent vertebrae and has a wedge-shaped profile with a plurality of footings and grooves located on the top and bottom surfaces.

CROSS-REFERENCE

The present application is a continuation of U.S. patent applicationSer. No. 11/469,851, which was filed on Sep. 2, 2006.

FIELD

The present application relates generally to an implantableintervertebral fusion device and, more specifically, to allograft bonedevices with an anatomical shape that effectively conforms to, andadheres to, the endplates of the adjacent vertebras. The presentapplication is also directed to methods of using a series of continuousfootings and grooves for strong mechanical attachment to the patientbone tissue.

BACKGROUND

The vertebral column is a bio-mechanical arrangement composed largely ofligaments, muscles, vertebrae, and intervertebral discs. Thebio-mechanical functions of the spine include: (1) support of the body,which involves the transfer of the weight and the bending movements ofthe head, trunk and arms to the pelvis and legs; (2) complexphysiological motion between these parts; and (3) protection of thespinal cord and nerve roots.

As populations age, it is anticipated that there will be an increase inadverse spinal conditions which are characteristic of aging. Forexample, with aging comes an increase in the degeneration of theintervertebral disc. Disabling mechanical pain resulting from discdegeneration is often treated surgically with an interbody fusion.

The primary purpose of the intervertebral discs, located between theendplates of the adjacent vertebrae, is to distribute forces betweenvertebrae, stabilize the spine, and cushion vertebral bodies. Thus theintervertebral disc acts as a shock absorber for the spinal column. Anormal intervertebral disc includes a semi-gelatinous component which issurrounded by an outer ring called the annulus fibrosus. In a healthyspine, the annulus fibrosus prevents the gelatinous component fromprotruding outside the disc space.

Spinal discs may be displaced or damaged as a result of disease, trauma,aging or injury to the spine. Frequently, the only relief from thedisability caused by degenerated spinal discs is a discectomy, orsurgical removal of the intervertebral disc followed by fusions of theadjacent vertebrae. The removal of the damaged or unhealthy disc withoutreconstruction would allow the disc space to collapse, resulting infurther instability of the spine, abnormal joint mechanics, prematuredevelopment of arthritis or nerve damage, in addition to severe pain. Toprevent the intervertebral space from collapsing, a structure must beplaced within the intervertebral space to provide support.

For example, in early spinal fusion techniques, bone material, or boneosteogenic fusion devices were simply placed between the transverseprocesses of adjacent vertebrae. The osteogenic fusion materialconsisted of cortical-cancellous bone which was not strong enough tosupport the weight of the spinal column at the instrumented level.Consequently, the spine was stabilized by way of a plate or a rodspanning the affected vertebrae.

For example, U.S. Pat. No. 4,604,995 assigned to Stephens, David C. andMorgan, Craig D., discloses “ a surgical implant for imparting stabilityto the thoraco-lumbar spine by fixation of the implant to the spine withsegmental spinal instrumentation, the implant comprising : a unitary rodhaving a generally rectangular configuration formed by a pair of spacedapart branches substantially mirror image duplicates of one another andsubstantially equally spaced apart along their entire length; a bightend piece interconnecting the branch pair at one end portion thereof;and a gate forming end piece connected to close the other end portion ofthe branch pair except for a small gate opening to provide access to thespace between the branch pair.”

With this technique, once the fusion occurs, the hardware maintainingthe stability of the spine becomes superfluous. There are other severaldisadvantages associated with the use of the abovementioned metalimplants. Solid body metal implants do not effectively enable bonein-growth which may lead to the eventual failure of the implant. Surfaceporosity in such solid implants does not correct this problem because itwill not allow sufficient in-growth to provide a solid bone mass strongenough to withstand the loads of the spine. Attention was then turned toimplants, or interbody fusion devices, which could be interposed betweenthe adjacent vertebrae, maintain the stability of the disc interspace,and still permit fusion or arthrodesis.

For example, U.S. Pat. No. 4,961,740 assigned to Centerpulse USA Inc.,discloses “ a fusion cage adapted for promoting fusion of one or morebone structures when bone-growth-inducing substance is packed into thefusion cage, comprising: a cage body defining a cavity with an innersurface; said cavity adapted to be packed with the bone-growth-inducingsubstance; said cage body defining an outer surface; means for definingthreads on the outer surface of the cage body and adapted for bitinginto the bone structure; said threads defining means including aplurality of threads which define valleys there between; a plurality ofperforations provided in the valleys of the threads for providingcommunication between the outer surface and the cavity in order to allowimmediate contact between the one or more bone structures and thebone-growth-inducing substance packed into the fusion cage”.

U.S. Pat. No. 5,026,373 assigned to Surgical Dynamics, discloses “amethod for surgically preparing two adjacent bony structures forimplanting a hollow cylindrical fusion cage that has an external,substantially continuous helical thread which defines a plurality ofturns with a valley between adjacent turns and that is perforated in thevalley between adjacent turns of the thread, said method comprising thesteps of: (a) drilling a pilot hole laterally between said bonystructures, (b) inserting a pilot rod into the pilot hole, (c) fitting ahollow drill over the pilot rod, (d) with the hollow drill, enlargingsaid pilot hole to form a bore that penetrates into the cortical bone ofeach of said bony structures, and (e) tapping a female thread into thewall of said bore, the crown of which female thread penetrates into thecancellous portion of each of said bony structures, which female threadcan mate with the helical thread of the fusion cage.”

The abovementioned intervertebral fusion device has substantialdisadvantages, however. The metallic supporting frame of the prior artfusion cages is not osteoconductive and therefore does not form a strongmechanical attachment to a patient's bone tissue. This can lead to graftnecrosis, poor fusion and poor stability. Moreover, many of thesedevices are difficult to machine and therefore expensive. Furthermore,the fusion cages may stress shield the bone graft, increasing the timerequired for fusion to occur. The abovementioned implants furtherrequires a special tool and additional preparation of the adjacentvertebral bodies to ensure fusion.

In addition, the use of bone graft materials in the prior art metal cagefusion devices presents several disadvantages. Autografts, bone materialsurgically removed from the patient, are undesirable because the donorsite may not yield a sufficient quantity of graft material. Theadditional surgery to extract the autograft also increases the risk ofinfection, persistent pain, and may reduce structural integrity at thedonor site.

U.S. Pat. No. 5,489,308 assigned to Zimmer Spine, Inc., discloses “animplant for insertion into a bore formed between opposing vertebrae of aspine where said vertebrae are separated by a spacing with a diskmaterial having an annulus disposed within said spacing, said implantcomprising: a rigid body having a leading end and a trailing end spacedapart by a longitudinal axis of said body; said body comprising at leastexposed threads disposed at least partially between said leading end andsaid trailing end; said threads selected to engage vertebra material anddraw said body along a direction of said axis upon rotation of said bodyabout said axis; said body having a hollow, generally cylindrical shellwith said threads disposed on an exterior surface of said shell; saidbody having means defining a chamber disposed within said body and saidbody is provided with a rib disposed within said cylindrical shell andextending radially inwardly toward said longitudinal axis, said ribdividing said chamber into a leading end chamber and a trailing endchamber, and said rib including at least a rigid extension extendingbetween and connecting diametrically opposed sides of said body; saidbody having means defining at least one opening formed through said bodyin communication with said chamber and with said opening extendinggenerally radially to said axis; and said body having a transversedimension generally transverse to said longitudinal axis and dimensionedso as to be greater than said bore for said body to urge said opposingvertebrae apart and to stretch said annulus upon insertion of said bodyinto said bore between said vertebrae with a portion of said bodyopposing a first of said opposing vertebrae and with an opposite side ofsaid body opposing a second of said opposing vertebrae.”

One problem with the implant devices of the type mentioned above is thatthey tend not to maintain the normal curvature of the spine. In ahealthy state, the cervical and lumbar areas of the human spine curveconvexly forward. Normal lordosis results, at least in significantmeasure, from the normal wedge-shaped nature of the spaces betweenadjacent pairs of the cervical and lumbar vertebrae, and the normalwedge-shaped nature of the intervertebral discs that fill these spaces.Loss of lordosis and proper intervertebral spacing may result in anincreased risk of degeneration to other intervertebral discs locatedadjacent to the fusion level due to the alteration of the overallmechanics of the spine.

A further problem with the abovementioned implant is that thecylindrical geometry of the engaging element tends to provide a smallarea of contact between the engaging element and the vertebrae. Thesmall engaging surface tends to contribute to subsidence or deformationof the cortical layer of the vertebrae adjacent to the engaging element.Moreover, the small engaging surface provides less contact between thebone graft material encased in the device and the adjacent vertebrae.Exposure of the bone graft material to the surface of the vertebrae isimportant because the greater the area of contact, the greater thepossibility of having a successful fusion.

U.S. Pat. No. 6,143,033 discloses “an allogenic intervertebral implantfor use when surgical fusion of vertebral bodies is indicated. Theimplant comprises an annular plug conforming in size and shape with theend plates of adjacent vertebrae and has a plurality of teeth positionedon the top and bottom surfaces for interlocking with the adjacentvertebrae. The teeth preferably have a pyramid shape or a saw-toothshape.” The teeth 105 of a prior art implant are shown in FIG. 1.

U.S. Pat. No. 6,986,788 discloses “an allogenic intervertebral implantfor use when surgical fusion of vertebral bodies is indicated. Theimplant comprises a piece of allogenic bone conforming in size and shapewith a portion of an end plates of the vertebrae and has a wedge-shapedprofile with a plurality of teeth located on top and bottom surfaces.”The teeth 205 of the implant 200 have a pyramidal shape, as shown inFIG. 2.

However, the implants are not sufficiently effective at preventingexpulsion of the implant. The surfaces of the implants, whetherpyramidal 205 or saw tooth 105, do not effectively provide implantstability.

In the light of the abovementioned disadvantages, there is a need forimproved methods and systems that can provide effective, efficient andfast intervertebral fusion device. Specifically, an intervertebralimplantable device is needed that conforms to the endplates of thepatient's adjacent vertebrae, maintains the normal disc spacing, andappropriate curvature of the spine. Further, an approach is needed thatmaximizes the probability of success of bone fusion, provides instantstability to the spine while fusion occurs, is easily implantable, andminimizes trauma to the patient and the possibility of surgical andpost-surgical complications.

SUMMARY

The present application relates to an implantable intervertebral fusiondevice for use when surgical fusion of vertebral bodies is indicated.The implant is comprised of bone conforming in size and shape with theend plates of the adjacent vertebrae and has a wedge-shaped profile witha plurality of footings and grooves located on the top and bottomsurfaces.

In one embodiment, the invention is an implantable intervertebraldevice, comprising a bone body substantially conforming in size andshape with the endplates of adjacent vertebrae wherein, the bone bodycomprises a top surface and a bottom surface and wherein each of saidtop and bottom surface comprises a macro-structure having plurality offootings and grooves that define a space, said space being covered by amicro-structure.

Optionally, the micro-structure mimics cancellous bone architectureand/or has osteoconductive or osteoinductive qualities. The device ismade of bone which is cut and machined into annular shapes. Optionally,the space defined by the grooves and footings is at least 3 mm.

Optionally, the footings comprise right triangles, have sharp ends,penetrate the endplates of the vertebrae, structurally degenerate tocreate an increased surface area for fusion, or have a minimum height of0.5 mm.

Optionally, the grooves allow bone in-growth or are positioned at thefront of each said footing. Optionally, the micro-structure has aroughness of the order of 100-250 micrometers. Optionally, the topsurface forms a convex curvature with its apex at the back of the bonebody.

Optionally, the bone body has a wedge-shaped profile to adaptanatomically to a curvature of a plurality of lumbar vertebrasendplates. Optionally, the bone body has a wedge-shaped profile to helprestore disc space height and spine curvature. Optionally, an angle ofthe wedge shaped profile lies between 7° to 9°.

Optionally, the bottom surface is a flat planar surface. Optionally, thebone body has lateral corners which are rounded or chamfered.Optionally, the bone body has a back which is rounded or chamfered.Optionally, the bone body has at least one side with a lateral squareguide for holding the bone body by a surgical instrument for anterior oranterior-lateral insertion.

Optionally, any of the devices have a bone body that comprises at leastone of allograft bone or xenograft bone. Optionally, any of the devicescan be used in any one of an ALIF, PLIF, ACF, or TLIF procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood when consideration is given tothe following detailed description thereof. Such description makesreference to the annexed drawings wherein:

FIG. 1 is a side view of the teeth of a prior art implant;

FIG. 2 is a perspective view of a prior art implant with pyramidalteeth;

FIG. 3 is a perspective view of one embodiment of the intervertebralfusion device of the present invention;

FIG. 4 is a top view of one embodiment of the intervertebral fusiondevice of the present invention;

FIG. 5 is a side view of one embodiment of the intervertebral fusiondevice of the present invention;

FIG. 6 is a side view one embodiment of the intervertebral fusion deviceof the present invention with details A and B;

FIG. 7 is a side view of detail A from FIG. 6;

FIG. 8 is a side view of detail B from FIG. 6;

FIG. 9 is a set of bones that are used in the fabrication of theintervertebral fusion device of the present invention;

FIG. 10 is a schematic diagram depicting the footings and grooves of theimplantable intervertebral fusion device of the present invention;

FIG. 11 is a schematic diagram depicting a set of lateral guides of theimplantable intervertebral fusion device of the present invention;

FIG. 12 is a schematic diagram of one embodiment of the surgicalinstrument for implanting intervertebral fusion device of the presentinvention;

FIG. 13 depicts the wedge shaped profile of the intervertebral fusiondevice of the present invention;

FIG. 14 depicts an anterior lumbar interbody fusion (ALIF) surgery forthe implantation of the intervertebral fusion device of the presentinvention;

FIG. 15 depicts the fusion of the new bone after the implantation of theintervertebral fusion device of the present invention has taken place;

FIG. 16 depicts a side schematic view of another embodiment of theintervertebral fusion device of the present invention; and

FIGS. 17A, 17B, and 17C are various configurations of footings that canbe used in the present invention.

DETAILED DESCRIPTION

The present application relates to an implantable intervertebral fusiondevice for use when surgical fusion of vertebral bodies is indicated.The implant is comprised of an allogenic cortical bone conforming insize and shape with the end plates of the adjacent vertebrae and has awedge-shaped profile with a plurality of footings and grooves located onthe top and bottom surfaces.

The top and bottom surface of the implant has a macro-texture and amicro-texture. The macro-structure is formed by a series of continuousfootings and grooves that cross the implant from side to side. Therelative placement of each footing and groove defines a surface uponwhich an osteoconductive and/or osteoinductive micro-structure may beapplied. The top surface of the implantable device is a convex surfacewith its apex at the back of the implant and the bottom surface is flatplanar surface or curved surface to match the topography of the endplate.

The lateral corners of the implantable device are rounded or chamferedin order to adapt anatomically to the vertebrae endplates curvature. Theback of the device is rounded or chamfered in order to facilitateinsertion of the implant. In one embodiment, the implant has a lateralguide or groove on at least one side for receiving a surgical instrumentfor implantation. The guide or groove runs in lateral direction toaccommodate a variety of surgical approaches. In another embodiment,resorbable and/or nonresorbable fixation devices, such as screws, couldbe placed on the endplates in front of the implant to improve initialfixation.

Referring to FIG. 3, a top view of the first embodiment of theintervertebral fusion device according to the present invention isdepicted. The intervertebral fusion device 300 conforms in size andshape with the end plates of the adjacent vertebrae between which thedevice 300 is to be implanted. The device 300 is made of an allograftmaterial which helps in the formation of new bone to fuse the twovertebral bodies together. In one embodiment, the intervertebral fusiondevice 300 is used as an implant deployed in an Anterior LumbarInterbody Fusion (ALIF) procedure. In another embodiment, theintervertebral fusion device 300 is used as an implant deployed in aPosterior Lumbar Interbody Fusion (PLIF) procedure. In yet anotherembodiment, the intervertebral fusion device 300 is used as an implantdeployed in an Anterior Cervical Fusion (ACF) procedure. In yet anotherembodiment, the intervertebral fusion device 300 is used as an implantdeployed in a Transforaminal Lumbar Interbody Fusion (TLIF) procedure.The intervertebral fusion device can be used in any region of the spine.

Referring to FIG. 9, a set of bones that are used in the fabrication ofthe abovementioned intervertebral fusion device is depicted. The bonescan be from any source, including animals such as cows or pigs, e.g.xenograft bone. In one embodiment, the intervertebral fusion device ismade of allogenic cortical bone received from human long bones. Thepieces of these cortical long bones 900 are cut perpendicular 902 to thebone axis and the marrow is removed to obtain annular shapes. Theannular rings are then machined using appropriate equipment, known topersons of ordinary skill in the art, and are finally cleaned forimplantation.

Referring back to FIG. 3, the intervertebral fusion device 300 comprisesa macro-structure 302 and a micro structure 303. The macro-structure 302further comprises a plurality of footings 304, 305 and grooves 306, 307that cross the intervertebral fusion device 300 from side to side. FIG.4 depicts the general ring structure of the intervertebral fusiondevice. In one embodiment, the dimensions 410, 420, 415 can be of anysize that would be appropriate for use in ACF, ALIF, and PLIFprocedures. In another embodiment, dimensions 410, 420 range from 2 mmto 6 mm, preferably 4 mm, and dimension 415 ranges from 2 mm to 8 mm,preferably 6 mm.

Referring to FIG. 5, an implant 500 is shown. The implant 500 comprisesa body 520 having a guide 515, a top surface 530, and a bottom surface540. Optionally, at least one of the top or bottom surface comprises aconvex depression 510 and a plurality of footings 505 and grooves 506that form a macro-structure for enabling adhesion between the implantand surrounding bone. An osteoconductive and/or osteoinductivemicro-structure, not shown, can be applied between the footings.

FIGS. 6-8 and 10 disclose a plurality of exemplary embodiments of themacro-structure. FIG. 6 depicts an implant structure 600 having amacrostructure 635 which is more particularly shown in details A and Bprovided in FIGS. 7 and 8 respectively.

The implant structure can be described by a plurality of dimensions,namely the distance between the highest portion of the top surface andthe lowest portion of the top surface 640; the anterior height 645; theanterior-posterior depth of the implant 605; the distance betweenfootings 665; the roughness of the microtexture coating 665; thedistance between the bottom surface and surgical instrument groove 655;the dome radius of certain structures 615, 625, 635 and themedio-lateral width (not shown). However, it should be appreciated thatthe values for these dimensions are not limiting and are provided as anenabling examples of how an implant could be practiced.

In one embodiment, an ALIF implant is designed with a distance of 2-6 mmbetween the highest portion of the top surface and the lowest portion ofthe top surface 640, which defines a lordosis angle of 5 to 13 degrees;a distance of 9-21 mm for the anterior height 645; a distance of 21-28mm for the anterior-posterior depth of the implant 605; a distance of2-6 mm between footings 665; a roughness of 100 to 250 microns for themicrotexture coating 665; a distance of 3 mm to 9 mm between the bottomsurface and surgical instrument groove 655; a dome radius of 0.1-2 mm,20-40 mm, and for 80-110 mm for structures 625, 615, 635 respectively;and a distance of 24-32 mm for the medio-lateral width (not shown). Theinstrument groove can be defined as having a width no greater thanone-third of the implant anterior height, which would yield a depthrange of 3 mm to 7 mm in this example, and a depth no greater than avalue which would leave the minimum implant wall thickness as at least 3mm.

In one embodiment, a PLIF implant is designed with a distance of 0-3 mmbetween the highest portion of the top surface and the lowest portion ofthe top surface 640, which defines a lordosis angle of 0 to 7 degrees; adistance of 7-16 mm for the anterior height 645; a distance of 20-26 mmfor the anterior-posterior depth of the implant 605; a distance of 2-6mm between footings 665; a roughness of 100 to 250 microns for themicrotexture coating 665; a distance of 3 mm to 9 mm between the bottomsurface and surgical instrument groove 655; a dome radius of 0.1-2 mm,20-40 mm, and for 80-110 mm for structures 625, 615, 635 respectively;and a distance of 7-11 mm for the medio-lateral width (not shown). Theinstrument groove can be defined as having a width no greater thanone-third of the implant anterior height, which would yield a depthrange of 2.33 mm to 5.33 mm in this example, and a depth no greater thana value which would leave the minimum implant wall thickness as at least3 mm.

In one embodiment, an ACF implant is designed with a distance of 0-5 mmbetween the highest portion of the top surface and the lowest portion ofthe top surface 640, which defines a lordosis angle of 0 to 10 degrees;a distance of 4.5-12 mm for the anterior height 645; a distance of 10-14mm for the anterior-posterior depth of the implant 605; a distance of2-4 mm between footings 665; a roughness of 100 to 250 microns for themicrotexture coating 665; a distance of 3 mm to 9 mm between the bottomsurface and surgical instrument groove 655; a dome radius of 0.1-2 mm,20-40 mm, and for 80-110 mm for structures 625, 615, 635 respectively;and a distance of 9-16 mm for the medio-lateral width (not shown). Theinstrument groove can be defined as having a width no greater thanone-third of the implant anterior height, which would yield a depthrange of 1.5 mm to 4 mm in this example, and a depth no greater than avalue which would leave the minimum implant wall thickness as at least 3mm.

Regardless of dimensions used, every adjacent footing 304 and groove 305defines an area upon which an osteoconductive and/or osteoinductivemicro-structure can be applied. The micro-structure preferably has aroughness of the order of 100-250 micrometer, although other roughnessranges, such as 50 to 1000 microns, may be employed. This microstructurehelps improve the initial stability of the intervertebral fusion devicedue to increased friction. The osteoconductive and/or oasteoinductivenature of the microtexture helps in the promotion of bone apposition. Inone embodiment, the microtexture comprises the coating described in U.S.Pat. No. 4,206,516, which is incorporated herein by reference. Inanother embodiment, the microtexture comprises the coating described inU.S. Pat. No. 4,865,603, which is also incorporated herein by reference.In one embodiment, the micro-structure mimics cancellous bonearchitecture.

Now referring to FIGS. 7 and 8, the diagram depicts the footings andgroove of the abovementioned implantable intervertebral fusion device.The footings 740, 750, 840, 850 have sharp protrusions which assist inthe penetration of the intervertebral fusion device into the vertebrasendplates and helps in the initial fixation of the implant. The initialmechanical stability attained by the footings 740, 750, 840, 850minimizes the risk of post-operative expulsion of the implant. Thegrooves 705, 706, 805, 806 adjacent to the footings 740, 750, 840, 850provide the long term fixation, after bone ingrowth happens in thegrooves 705, 706, 805, 806. The footings 740, 750, 840, 850 in unisonwith the grooves 705, 706, 805, 806 provide mechanical interlocksbetween the intervertebral fusion device and the endplates of thevertebrae. In one embodiment of the present invention, by fixing aminimum separation between the footings 740, 750, 840, 850 the number offootings on the surface of the implant is reduced. Therefore, the pointsof contact with the endplates are also reduced which enables higherpenetration of the footings 740, 750, 840, 850 into the endplates of thevertebrae.

In one embodiment, the footings 740, 840 have triangular protrusionswith tips defined by angle 815 of 35 to 45 degrees. In anotherembodiment, the footings 740, 840 have a height 720 of 0.3 to 0.7 mm. Inanother embodiment, the footings 750, 850 comprise a first portion witha minimum predefined elevation 730 above the groove. In anotherembodiment, the footings 750, 850 have a second portion with a minimumpredefined elevation 830 and a triangular protrusion with a tip definedas being in the range 715 of 35 to 45 degrees. It should be appreciatedthat, relative to the face of the implant, the footing protrusions areat right angles or tilted forward to ensure the implant resistsexpulsion by the vertebrae. This geometry of the teeth helps inpreventing movement toward the front of the implant.

In another embodiment, the footing is an elevated structure with a sharpportion thereto and defined by at least one angle 715, 815 in the rangeof 15 to 65 degrees. Referring to FIGS. 17A to 17B, alternative footingdesigns are shown. In one embodiment, shown in FIG. 17A, a first footing1701A has a triangular shape at an angle of less than 90 degreesrelative to the groove surface 1702A. Groove 1702A separates the firstfooting 1701A from a second footing 1703A. The second footing 1703A hasa protrusion with a face 1704A forming an angle of more than 135 degreesrelative to the groove surface. In another embodiment, shown in FIG.17B, a first footing 1701B has a triangular shape at a right anglerelative to the groove surface 1702B. Groove 1702B separates the firstfooting 1701B from a second footing 1703B. The second footing 1703B hasa protrusion with a face 1704B forming an angle of approximately 145degrees relative to the groove surface 1702B.

In another embodiment, at least one footing is in the shape of a pyramidand are right triangles with the opposite angles at 45° and itshypotenuse facing the back of the implant. In another embodiment, thefooting 1701C has a triangular shape, shown in FIG. 17C. Alternatively,footings may have a saw tooth shape with the saw tooth running in theanterior-posterior direction. For any given implant, the number offootings can be in the range of 4 to 8, although there is no limitationon the specific number of footings per implant.

It should be appreciated that, in one embodiment, the footings aredesigned to structurally degenerate, i.e. crumble, after implantinsertion, thereby increasing the surface area for fusion.

Referring to FIG. 11, a first lateral guide and the second lateral guideof the abovementioned implantable intervertebral fusion device isdepicted. The first lateral guide 1101 and the second lateral guide 1102are sized to receive surgical instrument such as an inserter forimplantation of implant. The first 1101 and second lateral guides 1102can be of any geometric shape. In one embodiment, they are rectangular.In another embodiment, the lateral guides 1101, 1102 are 1 mm deep and 3mm wide. In another embodiment, the lateral guides 1101, 1102 are of anysize that allows an intervertebral fusion device to be grasped by theimplantation instrument.

Referring to FIG. 12, one embodiment of the implantation instrument forimplanting the abovementioned intervertebral fusion device is depicted.The instrument comprises of handles 1201, 1202, and a set of two hooks1203, 1204 at the extreme end for grasping the lateral guides. Once thesurgeon is able to grip the lateral guides of the implant, the placementof the implant in the spinal column is carried out. In one embodiment,resorbable screws could be placed on the endplates in front of theimplant to improve initial fixation.

The dimensions of implant can be varied to accommodate a patient'sanatomy. However, the intervertebral fusion device of the presentinvention is preferably wide enough to support adjacent vertebrae and isof sufficient height to separate the adjacent vertebrae.

In one embodiment, a smaller implant would have a width of 27 mm and thefront to back length of 25 mm and a larger implant would preferably havea width of 32 mm and front to back length of 28 mm. The size of theimplant allows implants to be implanted using conventional open surgicalprocedures or minimally invasive procedures, such as laparoscopicsurgery or an ALIF procedure. This minimizes muscle stripping, scartissue in the canal, and nerve root retraction and handling. Inaddition, because the width is kept to a restricted size range and doesnot necessarily increase with implant height, taller implants can beused without requiring wider implants. Thus, facet removal andretraction of nerve roots can remain minimal.

In order to restore the natural curvature of the spine after theaffected disc has been removed, the intervertebral fusion device of thepresent invention has a wedge-shaped profile.

Now referring to FIG. 13, one embodiment of the wedge shape profile ofthe intervertebral fusion device of the present invention is depicted.The wedge shape 1301 of the device results from a gradual decrease inthe height from the front side to the back side. Thus, when implant isemployed in the lumbar region, in one embodiment, the angle 1302 formedby the wedge is preferably between 7° to 9°, so that the wedge shape canmimic the anatomy of the lumbar spine and it can adapt anatomically tothe curvature of the endplates of the lumbar vertebras.

In addition, to facilitate the insertion of implant and to adaptanatomically to the curvature of the vertebrae endplates, the lateralcorners of the device are rounded or chamfered. The rounded or chamferededges enable the intervertebral fusion device to slide between theendplates while minimizing the necessary distraction of the endplates.

Referring to FIG. 14, an anterior lumbar interbody fusion surgery forthe implantation of intervertebral fusion device of the presentinvention is depicted. The retroperitoneal approach for an ALIFprocedure involves an incision 1401 on the left side of the abdomen 1402and the abdominal muscles are retracted to the side. Since the anteriorabdominal muscle in the midline (rectus abdominis) runs vertically, itdoes not need to be cut and easily retracts to the side. The abdominalcontents lay inside a large sack (peritoneum) that can also beretracted, thus allowing the spine surgeon to access the front of thespine for implantation. In an alternate embodiment, endoscope procedurewhich involves surgery via several incisions can also be performed.

Although the intervertebral fusion device is a solid piece of allogeniccortical bone, the device can be provided with a hollow interior to forman interior space. This interior space can be filled with bone chips orany other osteoconductive surfacing or surface treatment, osteoinductiveor any other bone growth stimulation coating material to further promotethe formation of new bone. For example, FIG. 15 depicts the fusion ofthe new bone with the adjacent vertebrae after the implantation ofintervertebral fusion device has taken place. The intervertebral fusiondevice 1501 is sandwiched between the adjacent vertebrae 1502, 1503 andthe gradual bone in-growth takes place initially into the grooves of thedevice, and ultimately replaces the allograft bone structure.

Referring to FIG. 16, a top view of another embodiment of theintervertebral fusion device of the present invention is depicted. Insituations, where it is difficult to obtain a single section ofallogenic bone from which the implant is to be made, fabricating implantin two pieces, i.e. top 1601 and bottom portions 1602, allows smallersections of allogenic cortical bone to be used. A top connecting surface1603 and a bottom connecting surface 1604 define the interface betweenthe top 1601 and bottom 1602 portions.

As shown in the FIG. 16, the top 1601 and bottom 1602 surfaces, haveridges 1605 that mate with the grooves 1606 to interlock the top andbottom portions 1601, 1602. Preferably, ridges 1605 and grooves 1606 areformed by milling top and bottom surfaces 1603, 1604 in a firstdirection and then milling a second time with top and bottom surfaces1603, 1604 oriented with respect to the first direction. A pin 1607passing through aligned holes in top and bottom portions 1601, 1602serves to retain top and bottom portions 1601, 1602 together. Althoughpin 1606 can be made of any biocompatible material, pin 1606 ispreferably made of an allogenic bone. The number and orientation of pins1606 can be varied.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention.Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope of theappended claims.

1. An implantable intervertebral device, comprising: a bone bodysubstantially conforming in size and shape with the endplates ofadjacent vertebrae wherein, the bone body comprises a top surface and abottom surface and wherein each of said top and bottom surface comprisesa macro-structure having plurality of footings and grooves that define aspace, said space being covered by a micro-structure.
 2. The device ofclaim 1 wherein the micro-structure mimics cancellous bone architecture.3. The device of claim 1 wherein the micro-structure has osteoconductiveor osteoinductive qualities.
 4. The device of claim 1, wherein said bonebody is cut and machined into annular shapes.
 5. The device of claim 1,wherein said space is equal to at least 3 mm.
 6. The device of claim 1,wherein said footings comprise right triangles.
 7. The device of claim1, wherein said footings have sharp ends.
 8. The device of claim 1,wherein said footings penetrate the said endplates of the vertebrae. 9.The device of claim 1 wherein the footings structurally degenerate tocreate an increased surface area for fusion.
 10. The device of claim 1,wherein said footings have a minimum height of 0.5 mm.
 11. The device ofclaim 1, wherein said grooves allow bone in-growth.
 12. The device ofclaim 1, wherein said grooves are positioned at the front of each saidfooting.
 13. The device of claim 1, wherein the said micro-structure hasa roughness of the order of 100-250 micrometers.
 14. The device of claim1, wherein the top surface forms a convex curvature with its apex at theback of said bone body.
 15. The device of claim 1, wherein the bone bodyhas a wedge-shaped profile to adapt anatomically to a curvature of aplurality of lumbar vertebras endplates.
 16. The device of claim 1,wherein the bone body has a wedge-shaped profile to help restore discspace height and spine curvature.
 17. The device of claim 16, wherein anangle of the said wedge shaped profile lies between 7° to 9°.
 18. Thedevice of claim 1, wherein bone body has at least one side with alateral square guide for holding the bone body by a surgical instrumentfor anterior or anterior-lateral insertion.
 19. An implantableintervertebral device, comprising: a bone body substantially conformingin size and shape with the endplates of adjacent vertebrae wherein, thebone body comprises a top surface and a bottom surface and wherein eachof said top and bottom surface comprises a macro-structure havingplurality of footings and grooves that define a space, said space beingcovered by a micro-structure wherein the micro-structure hasosteoconductive or osteoinductive qualities.
 20. An implantableintervertebral device, comprising: a bone body substantially conformingin size and shape with the endplates of adjacent vertebrae wherein, thebone body comprises a top surface having a convex curvature with itsapex at the back of said bone body and a bottom surface and wherein eachof said top and bottom surface comprises a macro-structure havingplurality of footings and grooves that define a space, said space beingcovered by a micro-structure wherein the micro-structure hasosteoconductive or osteoinductive qualities.